Auxiliary cathode gas discharge device



Nov. 20, 1962 3,065,371

P. W. STUTSMAN AUXILIARY CATHODE GAS DISCHARGE DEVICE Filed July 22, 1949 2 Shams-Sheet 1 /NVENTOR PAUL W STUTSMAN iikv iii 3,h5,37l Patented Nov. 20, 1952 season AUXE'EZ AR! DISQHARGE DEVICE Paui W. Stutsman, Needham, Mass, assignor to Raythean Iompan a corporation of Deiaware Filed July 22, 1949, Ser. No. 106,179 11 Claims. (Cl. 3l3-19'7) This application relates to electron discharge devices and more particularly to gas-filled discharge devices capable of operating over a wide range of discharge currents.

In previous devices where a gas tube was desired which had high grid sensitivity, it has been found necessary to heat the cathode, either thermionically or ionically to create a supply of electrons upon which the control grid could act. Where it was required that the device should pass large currents, the power necessary to heat a cathode of suflicient size to pass said currents was considerable, and this heating power had to be applied during the stand-by condition of the tube to maintain the tube in readiness for firing. If it were desired that this particular tube at any time carry only small currents, it was still necessary that the large cathode be heated with the result that the cathode heating power would be large compared to the useful power realized in a load connected to the device.

Applicant provides herein a novel means of producing a device which will have high grid sensitivity and yet will require relatively low heating power. This is accomplished by providing for an auxiliary cathode of relatively small size which is maintained at an electron emitting temperature by any desired means such as an ionic discharge from said auxiliary cathode to a keep-alive anode, or by thermionic heating of the cathode. This auxiliary cathode is positioned between the main cathode and main anode and the electrons emitted therefrom are subject to control by the grid structure.

Thus when a small current is required from the discharge device, this current may be supplied by the auxiliary cathode. However, if a larger current is required, a voltage drop is created between the auxiliary cathode and main cathode due to current flow in an impedance connecting said cathodes with the result that positive ions will fall onto the main cathode heating the same and initiating a self-sustaining auxiliary discharge between the main cathode and main anode. Thus it may be seen that during the periods when large currents are not drawn by the device, the main cathode remains cold and when large currents are required, the main cathode is heated by ionic bombardment to provide the necessary electrons for the discharge.

By the use of a hollow cathode for the main cathode, applicant has produced a structure which will conserve the heat of the cathode, and in addition will tend to conserve the supply of electron emissive material of the cathode sincematerial torn or sputtered off from the main cathode by the discharge will to a large extent redeposit on the main cathode. Also, by the use of this of main cathode which is rugged and rigid, the tube may be placed in any position during operation without detrimental results.

By means of adequate grid shielding of the anode comprising a glass tube surrounding the anode rod and a cupshaped grid covering the end of the anode rod and glass tube, relatively high anode to cathode voltages may be applied to the device without breaking down the space therebetween.

Also, applicant discloses herein circuits particularly adapted to utilize this discharge device. Since a feature of the device is the ability thereof to operate at either low or high discharge currents, a circuit is provided whereby the load may be changd to accomplish difierent purposes with the different currents.

T he particular details whereby the foregoing advantages are obtained will now be described in detail, reference being had to the accompanying drawings wherein:

FIG. 1 represents a longitudinal cross-sectional view of a device embodying the principles of this invention taken along line 1-4. of FIG. 2;

FIG. 2 illustrates a transverse cross-sectional view of the device shown in MG. 1 talren along line 22 of FIG. 1 illustrating the details of the auxiliary cathode structure;

H6. 3 is a transverse cross-sectional view of the device shown in FIG. 1 taken along line 3--3 of FIG. 1',

FIG. 4 illustrates a circuit utilizing the device of FIGS. l-3 wherein a method of ionically heating the auxiliary cathode is disclosed; and

PEG. 5 illustrates another circuit utilizing the device of FiGS. 13 wherein means are provided for thermionically heating the auxiliary cathode.

Referring now to F168. 1, 2 and 3, there is shown a glass envelope 2% consisting of a tube one end of which is pressed together as at 21 and through which extends a plurality of lead-in wires. The other end of the glass tube 29 is curved together and contains at its center a mass of glass 22 which is used to seal the envelope after filling of the envelope with the correct gaseous medium. Extending upward from the glass press 21 inside envelope 2d are three glass tubes 2.3, 24 and 25 whose axes are all parallel and lying in the same plane and spaced an equal distance apart. The center glass tube 24 extends slightly less than one-third the length of envelope 20. Inside the glass tube 24 which is hollow, is an anode rod 25 which extends from the open end of the glass rod 24 toward the glass press 21 through a spacer 27 consisting of a wire spirally wrapped around anode rod 26. Anode rod 26 is then joined, for example, by Welding to a lead-in wire 28 which extends through the glass press 21.

The end of the tube M which is open, is covered by a cup-shaped grid 29 of wire mesh which may be made of 60 x 60 strands per inch screening using .005 inch nickel wire. The diameter of the cup-shaped grid 29 is slightly larger than the diameter of the glass tube Z-t and extends for somewhat more than one diameter of the glass tube over the end of said rod. The bottom of said cup-shaped grid 29 is in close proximity but not touching the end of the tube 24 and the anode element 2 6. Cup-shaped grid 29 is supported by being attached as by welding to a strap 30 at the lip of said cup-shaped grid. The strap 3t} extends around the tubes 23 and 2-5 thereby rigidly supporting the grid 29. The tubes 23 and 2 5 are somewhat longer than the tube 24 and extend further into the envelope 2!) past the end of tube and the grid 29. A lead-in wire 31 is attached to the strap 3% as by welding and extends along the side of envelope 2% through the glass press 21.

Extending the length of rods 23 and 25 which are hollow, is a pair of support rods 35 which are butt welded to lead-in members 31: extending through the glass press 21. The rods 35 contain spacers 37 thereon similar to the spacer 27 on anode rod 26. The rods 35 extend out of the open ends of the glass rods 23 and 25 for a distance equal to approximately half the diameter of envelope and then pass through a mica plate 33. The mica plate 30 is flat and has a shape conforming to the inside contour of the envelope 2d at a section taken at the right angles to the rods 35. Tabs 35a are welded to rods 35 on both sides of plate 38, thereby preventing movement of plate 38 on rods 35.

A cathode 39 is supported between the rods 35 in the space between the mica plate 38 and the bottom of the cup-shaped grid 32. This cathode consists of a helicallywound wire coated with electron emissive material, the diameter of said helix being approximately equal to the diameter of the glass tube 24. One end of said helicallywound wire is attached as by welding to one of the rods 35 and the other end to the other rod 35.

Between the cathode 39 and the cup-shaped grid 32 there is positioned a keep-alive grid 49. This grid is a semicylindrical piece of screening of the same type used to make grids 2% and 32.. The axis of the semicyiindrical screen is approximately concentric with the axis of the helical cathode 39. The diameter of the cylindrical screen all is slightly greater than the helix of the cathode 39 such that grid 4% is in close proximity with the cathode 39. The grid 46 is supported at each end by straps 41 welded thereto and which are attached to bands 42 mounted on the tubes 23 and 25. The grid 40 is connected to a lead-in wire 43 which extends along the side of envelope 2%) through the glass press 21.

The mica support member 38 has a hole 53 therein approximately equal in diameter to and concentric with the inside diameter of the glass anode shielding tube 24. A second mica member 54 similar in shape to the mica member 38 and having a hole 55 therein somewhat larger in diameter than the hole 53 in mica member 38 but concentric therewith, is positioned parallel with the member 38 and spaced slightly therefrom on the opposite side of member 38 from the cathode 39.

Above mica member 54 is another cathode 56 comprising a metallic cylinder 57 which may be, for example, of nickel whose diameter is somewhat smaller than the diameter of envelope 2-8 and whose length is somewhat greater than its diameter. The lower end of the cylinder 57 rests on the mica member 54 and has an end plate 58 which may be of nickel and which has a hole 59 therein, concentric with holes '53 and 55, whose diameter is somewhat less than the inside diameter of the rod 24. The upper end of the cylinder 57 is sealed by a second end plate 60, and rests against a mica member 61 similar to member 54. A member 62 is attached to the center of end plate 60 and extends through the hole in mica member 61. Attached to the member 62 is a lead-in member 63 which extends through the glass seal 22 in the upper end of envelope 20. Inside the cylinder 57 is wound a wire 64 which contains electron emissive material said wire completely covering the inside of cylinder 57.

Referring now to FIG. 4, there is shown a circuit utilizing the discharge device of FIGS. l3 comprising a first load 65 connected between anode 26 and B+ and a second load 66 in parallel with load 65. A relay 67 is provided having a pair of contacts 655 in series with the second load 66 such that when relay 67 is energized from any desired source, contact 68 will open disconnecting load 66 from the circuit.

Main cathode 56 is connected to ground, and the two leads 36 of auxiliary cathode 39 are connected together and to ground through a resistor 69 to ground. Ke palive electrode 46 is connected to B+ through a voltage dropping resistance 7% which may be on the order of .500 ohms. The control grid 29 is connected to a signal input source through a DC. blocking condenser '71 and to ground through a biasing battery 72 and a grid load resistor 73.

In operation the auxiliary cathode 39 is heated by an ionic discharge therefrom to the electrode 46. This discharge will provide a reliable source of electrons with a discharge current of, for example, 30 milliamperes. However, lower keep-alive currents may be used if desired. When the load selector relay 67 is energized and the second load 66 is disconnected from the anode circuit, the impedance of the first load 65 is of such a value that a discharge in the tube will be limited to a current on the order of 100 milliamperes. This load impedance would be on the order of 1500 ohms for a B-}- voltage of 150 volts. The value of resistor 6% is such that when a discharge current of milliamperes is drawn through load 65, the voltage drop across resistor 69 due to said discharge current is insutficient to cause ions from the discharge to fall on cathode 56 with enough velocity to create a selfsustaining arc. The value of resistor 69 will vary with the particular tube design, and for the particular design illustrated herein may be on the order of 100 ohms. If it is desired at any time to use the tube to feed a large current to a load, for example, to the second load 66, the contacts 68 are closed by deenergization of the relay 67. The impedance of the load 66 is on the order of a few ohms such that 100 amperes passing through the load will create a voltage drop thereacross on the order of volts. When the tube is fired and the larger current is drawn from cathode 39, this current passing through resistor 69 will create an initial drop between the cathodes which is large compared with the drop across the load, so that the potential of the auxiliary cathode 2 is raised well above the main cathode 56. Thus many positive ions will fall into the cathode 56 and release secondary electrons in sufficient quantity to cause the anode-auxiliary cathode plasma to extend to the main cathode 56, whence a self-sustaining are, capable of carrying high amperage current is produced.

Referring now to FIG. 5, there is shown a circuit whereby the auxiliary cathode 39 may be thermionically heated. The ends of cathode 39 which as shown in FIG. 1 terminate in two lead members 36, are connected to the secondary winding 74 of a filament transformer 75, the primary 76 thereof being connected to a suitable voltage source. Secondary winding 74 is center tapped, the center tap being connected to ground through the resistor 69. Since the ionic discharge between the cathode 39 and the electrode 4-0 is no longer required for heating purposes, electrode 4% is connected to grid 29 through a current limiting resistor 77. However, if desired, the electrode 4t) could be eliminated altogether. Obviously the loads and switching arrangement illustrated in FIG. 4 may be used in the modification of FIG. 5 and are illustrated diagrammatically therein by the box 78. The remaining elements of FIG. 5 are similar to those of FIG. 4 and the method of operation, except for the method of heating auxiliary cathode 39, is identical.

Since this type of tube does not use a main cathode which is liquid, such as mercury, an inert gas filling may be used. The filling used herein is xenon; however, argon and krypton may be used. Since these gases have relative- 1y low thermal conductivity, relatively high pressures, for example, 30 millimeters of mercury, may be used which tend to inhibit the loss of cathode coating due to sputtering. Further, due to their relatively low ionization potential and high secondary electron yield, due to their large mass, a relatively low starting voltage is produced.

Thus it may be seen that applicant has provided a gasfilled tube which may be operated with either an ionically heated or a directly heated auxiliary cathode, which has a relatively high grid sensitivity, and which will pass currents ranging from steady fractional currents to high amperage peak currents, with the permissible peak currents far exceeding the current capacities of the small auxiliary cathode which requires only low heating power.

This completes the description of the embodiments of the invention illustrated herein. However, many modifications thereof will be apparent to persons skilled in the art, for example, a plurality of grids similar to grid 29 might be employed as well as different spacing and positioning of the tube elements. Therefore, applicant does not Wish to be limited to the specific details of the modifications described herein except as described by the appended claims.

What is claimed is:

1. An electron discharge device comprising an envelope containing a gaseous medium, a cold cathode, an anode comprising a rod-shaped member, a cylindrical insulating member positioned around said anode, one end of said insulating member being open thereby presenting a portion of said anode to said cathode, a grid substantially covering the open end of said insulating member, and an auxiliary source of free electrons positioned in the space between said cathode and anode.

2. An electron discharge device comprising an envelope containing a gaseous medium, an anode, a cold, hollow cathode having electron emissive material on the interior surface thereof, a grid substantially shielding said cathode from said anode, and an auxiliary thermionic source of free electrons positioned in the space between said cathode and anode.

3. An electron discharge device comprising an envelope containing a gaseous medium, an anode, a cold cathode, a grid substantially shielding said cathode from said anode, and an auxiliary source of free electrons positioned in the space between said cathode and anode comprising a second cathode and means for heating said second cathode comprising an electrode spaced in close proximity with said second cathode and adapted to produce a discharge between said second cathode and said electrode upon the application of a potential thereacross.

4. An electron discharge device comprising an envelope containing a gaseous medium, an anode, a cold, hollow cathode, a grid substantially shielding said cathode from said anode, and an auxiliary source of free electrons positioned in the space between said cathode and anode comprising a second cathode and means for heating said second cathode to thermionic emission temperatures, independent of the magnitude of said emission.

5. An electron discharge device comprising an envelope containing a gaseous medium, a first cathode, a first anode, and means for maintaining an electron discharge in the space between said first anode and said first cathode independent of electron flow from said first cathode to said first anode comprising a second cathode adapted to be ionically heated and second anode between said first cathode and said first anode, said second cathode being supported on substantially shielded lead-in members.

6. An electron discharge device comprising an envelope containing a gaseous medium, a first cathode, a first anode surrounded by a sleeve of insulating material, a cupshaped grid surrounding said insulating sleeve and said first anode, and means for maintaining an electron discharge in the space between said first anode and said first cathode independent of electron flow from said cathode to said anode comprising a second cathode and second anode between said first cathode and said first anode, said first cathode having an electron emitting capacity substantially greater than said second cathode.

7. An electron discharge device comprising an envelope containing a gaseous medium, a hollow cathode, an anode and means for maintaining an electron discharge in the space between said anode and said cathode independent of electron flow from said cathode to said anode and an insulating shield spaced between said cathode and said discharge maintaining means, and having a hole therein.

8. An electron discharge device comprising an envelope containing a gaseous medium, a first cathode, a first anode surrounded by a sleeve of insulating material, a cupshaped grid surrounding said insulating sleeve and said first anode, and means for maintaining an electron discharge in the space between said first anode and said first cathode independent of electron flow from said cathode to said anode comprising a second cathode and second anode between said first cathode and said first anode, said first cathode having an electron emitting capacity substantially greater than said second cathode and being supported from one end of said envelope, said second cathode being supported by lead-in means from the other end of said envelope, insulating means surrounding said lead-in means in the vicinity of said first anode, and said second anode being supported from said insulating means.

9. A gaseous discharge device comprising a large area cathode, a small area anode opposite said cathode and defining a gap therewith, a control electrode in said gap, means maintaining a continuous keep alive discharge in said device, means biasing said control electrode for injecting electrons from said keep alive discharge into the vicinity of said anode, and means biasing said anode to allow breakdown in the vicinity of said anode only following the injection of the electrons from said keep alive discharge.

10. A gaseous discharge device comprising a large area cathode, a small area anode opposite said cathode and defining a gap therewith, a large area control electrode in said gap and having an aperture therein, means maintaining a continuous keep alive discharge in said device, said discharge being in alignment with said main gap, means biasing said control electrode for injecting electrons from said keep alive discharge through said aperture into the vicinity of said anode, and means biasing said anode to allow breakdown in the vicinity of said anode only following the injection of the electrons from said keep alive discharge.

11. A gaseous discharge device comprising a large area cathode, a small area main anode opposite said cathode and defining a gap therewith, an auxiliary anode in said gap adjacent said cathode, a control electrode in said gap adjacent said main anode, means biasing said auxiliary anode with respect to said cathode to maintain a discharge therebetween, means biasing said main anode relative to said cathode at a potential suflicient to sustain a discharge across said gap but insufficient to efiect breakdown of said gap, and means biasing said control electrode controlling the injection of electrons from said discharge into the vicinity of said main anode to effect breakdown of said gap.

References Cited in the file of this patent UNITED STATES PATENTS 1,551,970 Schafer Sept. 1, 1925 1,967,009 Hund July 17, 1934 2,007,542 Lubcke July 9, 1935 2,062,268 Knowles Nov. 24, 1936 2,270,324 Marshall Jan. 20, 1942 2,331,398 Ingram Oct. 12, 1943 2,435,246 Stutsman Feb. 3, 1948 2,468,417 Stutsman Apr. 26, 1949 2,479,846 Lalewicz Aug. 23, 1949 

